Adducts of diaminodiphenyl compounds and diglycidyl ethers of polyhydric phenols are described in U.S. Pat. No. 4,330,659. These hardeners for epoxy resins exhibit improved processability in prepregging compared with unmodified diaminodiphenyl sulfones, but suffer from the disadvantage that the cured resins exhibit comparatively low modulus and strength and the decreased thermal performance (i.e. modulus retention at temperatures greater than 100.degree. C.). The melt viscosity of compositions containing the foregoing adducts is considerably higher in comparison to compositions containing the unmodified diaminodiphenyl sulfones. Due to the aforementioned disadvantages, these adducts cannot be used in certain processes such as resin transfer molding or filament winding.
Accordingly, it is a primary object of the present invention to provide a modified hardener system for epoxy resins which overcomes the disadvantages of the prior art unmodified diaminodiphenyl sulfones and the adducts thereof with diglycidyl ethers of polyhydric phenols in accordance with U.S. Pat. No. 4,330,659.
It is a further object of the present invention to provide a modified hardener system for matrix epoxy resins for prepregging, laminating, filament winding and resin transfer molding.
It is a still further object of the present invention to provide a modified hardener system which provides cured epoxy resin systems exhibiting improved modulus, mechanical strength and thermal performance.
Various other objects and advantages of the present invention will become apparent from the following description and examples.
It has now been surprisingly discovered that the reaction product of diaminodiphenyl sulfone and cycloaliphatic diepoxides provides hardeners for epoxy resin systems which epoxy resin system cured therewith exhibit improved performance characteristics, such as modulus and strength retention at 100.degree.-150.degree. C.